The invention relates to a printed circuit board comprising one or more opto-electronically active luminous elements on the basis of electroluminescent systems, which elements can be made to emit light by applying a suitable supply voltage, thus converting passive printed circuit boards for interconnecting components into active multifunctional printed circuit boards, and the invention also relates to the application and method of manufacturing such a printed circuit board.
Thus, the invention relates to printed circuit boards with electroluminescent luminous fields, which are made to emit light upon application of a suitable voltage and frequency.
To manufacture electroluminescent arrangements by means of known printing techniques, electroluminescent coloring substances are known which are generally prepared on the basis of inorganic substances, such as, in particular, highly pure ZnS, CdS, Zn.sub.x Cd.sub.1-x S, etc., compounds of the II and VI groups of the periodic system, which are customarily doped or activated with Cu, Mn, Ag, etc. Customary colors include yellow, green, greenish blue, bluish green and white. In accordance with the state of the art, such electroluminescent pigments, whose diameters range typically from 15 .mu.m to 60 .mu.m, are admixed in micro-encapsulated or non-encapsulated form with the various printing dyes, while taking into account the specific hygroscopic properties of the ZnS pigments. The binding agents used adhere well to so-called conductive ITO films (Indium-Tin-Oxide films), they are good insulators, they enhance the dielectric properties and hence improve the dielectric strength at high electric field intensities. The binding agents should additionally exhibit a good water-vapor resistance in the cured state, protect the phosphor pigments and extend the service life.
Customarily, such electroluminescent dyes, which are commonly also referred to as phosphor pastes, are applied to transparent synthetic-resin foils or glasses by means of screen printing or other coating methods such as spread coating, roller coating, etc. The synthetic-resin foils, etc., comprise a substantially transparent electroconductive coating serving as the electrode for the viewing side. Subsequently, the dielectric and the rear-side electrode are manufactured by means of printing and/or lamination techniques. Such an electroluminescent arrangement is known, for example, from DE-A-44 30 907.
Often the order of the manufacturing process is reversed, as described, for example, in DE-A-43 19 441, in which first the rear-side electrode is manufactured or use is made of a rear-side electrode in the form of a metallized foil on which the dielectric is applied or is already present thereon in the form of a coating. Subsequently, the phosphor paste and the transparent, electroconductive upper electrode is provided, for example, in the form of an ITO paste. Customarily, such a system is further covered with a transparent covering foil, thus protecting it against water vapor and mechanical damage.
Customary ITO-paste coatings (or also coatings of tin oxide, etc.) which are provided by screen printing have the advantage that they can be provided in almost any desired shape, however, they have the disadvantage, compared to vapor-deposited or sputtered transparent and electroconductive films, that their optical transparency is smaller and their surface conductivity of generally several 100 Ohm per square (.OMEGA./.box-solid.) is substantially smaller compared to several 10 Ohm per square in the case of ITO-polyester foils and a few Ohm per square in the case of ITO-coated glasses, whereby in the case of glasses, additionally, pastes can be used, for example In.sub.2 O.sub.3 /SnO.sub.2, which must be fired at temperatures above 500.degree. C., leading to an optical transparency beyond 95% at a film thickness of only 0.25 .mu.m, and a conductivity in the case of a single coating of 500 to 1000 Ohm per square.